The XRD patterns of the as-prepared samples through the
simple precipitation method are shown in Fig. 1. All of the
diffraction peaks are in agreement with the JCPDS file of ZnO
(JCPDS No. 5-664), which can be indexed as a hexagonal phase of
ZnO. The sharp diffraction peaks manifest the high crystallinity of
the sample. The absence of impure phase suggested that the
products had high purity. Fig. 2 shows SEM images of the asprepared ZnO with nanostructure. A large quantity of snowflake with different shapes has been observed in SEM image of Fig. 2a. Furthermore, a magnified SEM image shows the integrated morphology of an individual snowflake-like ZnO nanostructure
(Fig. 2b). The size of these snowflakes is about 1 mm, which is made of nano-platelets with uniform thickness (20–30 nm).